1. Field of the Invention
This invention relates to semiconductor photodetector devices and more particularly to enhancing the photocurrent gain of a photodetector by applying a bias voltage across it.
2. Terms of Art
In this specification a number of terms of art are used and should be taken to have the following meanings:
(i) The term amorphous encompasses not only traditional amorphous materials that lack long-range atomic order, but also includes nano- or microcrystalline materials that contain tiny crystallites within a surrounding disordered matrix. PA1 (ii) Chopped beam of light encompasses any beam of light which is periodically and briefly interrupted or otherwise modulated to cause the beam of light to be intermittent. Traditionally the term chopped light designates a repetitively on/off condition of the beam. As used herein, however, the term should also be taken to include intermittent light produced by other means. PA1 (iii) The term dark current means the current flowing through a photodetector under action of an applied voltage when no light is incident on the detector. PA1 (iv) The flat band voltage of a photodetector is the voltage that must be applied to the detector to overcome the built-in or inherent electric potential across a semiconductor photodetector. PA1 (v) The photocurrent gain of a photodetector is defined by the equation: EQU G(.lambda.)=.DELTA.J.sub.ph (.lambda.)/e.PHI.(.lambda.) PA1 (i) a substrate; PA1 (ii) first electrode means formed on said substrate; PA1 (iii) a body portion supported by said first electrode, said body portion including at least two monolithic, contiguous amorphous silicon regions wherein one of said regions is doped to be of a first conductivity type and the other of said regions is an intrinsic region and wherein a high number of defects are present at or near the interface between said two regions; PA1 (iv) second electrode means formed over said body portion; and PA1 (v) means to apply a forward bias voltage across said detector. The forward bias voltage must be greater than the flat band voltage of the detector and be sufficient to bias the detector into the space charge limited regime in which electrons, injected at the second electrode, are blocked by a potential barrier formed near the interface between the contiguous regions.
where .DELTA.J.sub.ph (.lambda.) is the change in the photogenerated current occurring in response to a signal light of wavelength .lambda., .PHI.(.lambda.) is the flux density of the signal light and e is the charge of an electron.